The following abbreviations are herewith defined:
3GPPthird generation partnership projectATallocation table (also called physical downlink shared controlchannel PDCCH)C-RNTIcell radio network temporary identifierDLdownlink (node B to UE)DRXdiscontinuous receptionGPRSgeneral packet radio serviceGSMglobal system for mobile communicationHOhand overIMSinstant messaging serviceLTElong term evolutionMACmedium access controlNode Bbase stationPTCCHpacket timing advance control channelRACHrandom access channelRLIDradio link identifierRNCradio network controlRRCradio resource controlSCHshared channelTAtiming advanceTBFtemporary block flowUEuser equipmentULuplink (UE to node B)UMTSuniversal mobile telecommunications systemUTRANUMTS terrestrial radio access networkE-UTRANevolved UTRAN, also referred to as UTRAN-LTE and as3.9GVoIPvoice over internet protocol
UTRAN-LTE is defined as a packet-based transmission system only. This implies that there will not be a so-called dedicated connection mode (or circuit switched mode) as exists in some currently deployed systems.
As currently defined the uplink air interface resources are divided between an UL-SCH and a contention based RACH. A Node-B may provide an allocation on the UL-SCH if the UE can be identified (such as with RLID/C-RNTI) and if the TA of the UE has been so recently controlled by the Node-B such that it can be considered to be valid. If the UE has no valid TA it is not allowed to transmit on the UL-SCH. The random access procedure may be used by the UE for initial network access, for TA adjustment, for transfer from LTE-IDLE to LTE-ACTIVE state, for uplink resource requests and during HO. One of a synchronous or non-synchronous random access procedure is used, depending on the validity of UE's TA.
Further reference with regard to the RACH channel can be made to, for example, Annex B of 3GPP TR 25.813, V0.8.3, 3rd Generation Partnership Project, Technical Specification Group Radio Access Network; Evolved Universal Terrestrial Radio Access (E-UTRA) and Evolved Universal Terrestrial Radio Access Network (E-UTRAN), and Radio interface protocol aspects (Release 7).
One proposal for UTRAN-LTE is that the UE will receive the UL-SCH resource allocations from the network through an AT, where the UE would receive the AT at certain instants in time determined at least in part by the current DRX period of the UE (which may be defined by the network).
It should be noted that in the general case resource(s) are assigned to the UE by the network through the use of DL control signaling. The exact format and content of this control signaling is not particularly germane to an understanding of the invention, and in fact may be subject to revision.
However, if the currently used DRX period of the UE is long (e.g., seconds) the TA used by the UE before the DRX period may no longer be valid for use in transmission in the UL-SCH. If the UE no longer has a valid TA it is not allowed to transmit in the UL-SCH before the UE has received a new TA value from the network.
More generally, if the time from the last update of the TA is long, however the TA may be updated, then the TA may not be valid. The use of DRX periods to ascertain the potential validity or invalidity of the current TA of the UE is but one non-limiting example.
It has been proposed that the procedure for achieving a valid TA (when no valid TA is available) includes transmission by the UE on the non-synchronized RACH channel. However, this approach, which utilizes a contention based resource (where the possibility of collisions, backoffs and re-transmissions may occur), may introduce an undesirable and unpredictable delay.
Another issue relates to a requirement in 3.9G that the UE in the Active state shall always be UL synchronized. Such a requirement would in practice mean that there would be a need for constant DL/UL transmissions in order to allow the network to maintain the UL synchronization (TA) of the UE up-to-date, and could require scheduled DL/UL transmission for no other reason than keeping the UE TA current. As can be appreciated, this approach is not efficient in terms of UE power consumption and bandwidth utilization.
Yet another issue relates to whether it is really necessary for all connection types and services to maintain UL synchronization at all times. One justification for maintaining UE UL synchronization is that there is a need for fast connection setup time (short delay), and another is to maintain a constant regular UL/DL data flow with short intervals (e.g., VoIP). In other situations, however, such as normal WEB browsing or email download, the setup time may not be as important and the data may be transmitted in a bursty (aperiodic) manner.
It is noted that in the currently deployed GSM HO procedure, when the UE receives a HO command to a new cell and does not have a valid TA for the new cell, the UE is not allowed to transmit a normal UL burst in the new cell. Instead, the UE must transmit a shorter duration burst that leaves a large part of the time slot as a guard time or guard band around the burst. The network measures the propagation delay from the received short burst and sends an appropriate TA value to the UE. The UE can then start to use the newly assigned TA value when transmitting a normal UL burst.
The use of the PTCCH in the GPRS is another already deployed procedure for assuring that the UE has UL synchronization. However, the use of this procedure is only valid when the UE has an active TBF, which means that there is an already established UL/DL connection between the network and the UE.